In an attempt to make sense of the
vast array of data on propeller cost,
performance, durability, appearance,
and other factors, I decided to do a
survey among builders, beginning at
Sun ’n Fun 2009. I followed up by
quizzing builders in my local EAA
chapter and others with whom I
had contact. My main purpose was
to learn why individuals choose a
certain design, and which criteria
are important to them. This article is
primarily about propellers for high-performance aircraft, since propeller
choices are much more involved
for this class of aircraft than for the
low-and-slow designs. Most of the
simpler airplanes use fixed-pitch or
ground-adjustable props. Kit manu-
facturers for this class of aircraft
often recommend a particular propeller with which the company has
had good success.
But when choosing a propeller
for a high-performance experimental airplane, the choices are many,
and there are a lot of variables. After
communicating with many builders, I ended up with a bewildering
array of reasons for liking a given
prop. Performance was often the primary consideration, but performance
means different things to different
people, depending on individual
requirements. As one might expect
for high-performance airplanes, takeoff, climb, and speed were primary
considerations. Other factors men-
tioned were rain resistance, ground
clearance, and smoothness. Durability with respect to aerobatic stresses
was important to some.
For all experimental aircraft types
surveyed (126 in all), the percentages
of metal, composite, and wood were
67 percent, 21 percent, and 12 percent, respectively. High-performance
designs made up 103 out of 126, or
82 percent. Wooden props made up
only 6 percent of the propellers on
this class of aircraft, but 39 percent
on the lower-performance designs.
Obviously, none of the lower-performance airplanes sported constant-speed propellers. My survey was not
extensive enough to take those figures as representative of the entire
fleet of experimental aircraft.
Some fairly recent changes in blade
design have improved both appearance and performance. This development was ushered in by modern
composite technology and research
on blade design. Manufacturers of
composite blades are not limited
to the straight shapes of previous
wood and metal designs, and as a
result we have seen improvements
in speed, smoothness, and quietness
in addition to better looks. Form follows function, even in propellers. For
example, research has shown aerodynamic advantages in a more swept
look, which, in a propeller, is analogous with the swept wing of a supersonic fighter. This is embodied in
the Hartzell scimitar propeller and in
the MT designs, among others. And
yet bold, new designs that appear to
break many of the rules continue to
be proposed, such as the Paul Lipps
propeller (see Go Direct, page 58),
with claims of superior performance.
It’s encouraging that research is continuing on propeller design.
I noticed that many builders
today mention appearance as a factor in choosing a propeller. Gone
are the days when your two color
choices for a propeller were either
natural laminated wood—usually
with white tips—or a dull, battle-
ABOVE: Hatcher Ferguson of Roanoke,
Virginia has a Whirl Wind composite
propeller on his RV-7A.
LEFT: Martin Albrecht, vice president and
general manager of MT Propeller, says the
company knows of no in-flight failures of
their blades in their 29 years.
